Compressor assembly

ABSTRACT

A compressor assembly includes compressor means having an inlet, an outlet and a means for drawing air through the inlet and exhausting compressed air through the outlet, rotary drive input means, and gear means for changing the speed of the rotary drive input means and having an input connected to the rotary drive input means and an output driving the compressor means, the gear means comprising planetary gear means.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of United Kingdom (UK) PatentApplication No. 0919643.7, filed on Nov. 10, 2009, and entitledCompressor Assembly, which is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to compressors, and more particularly to acompressor assembly.

Tankers carrying dry bulk materials, such as cement, flour, plasticpellets, etc., are unloaded by pressurizing the tank with air, typicallyup to 3 bar absolute pressure. For a road tanker the preferred mountingof the compressor is normally within the chassis of a towing tractorunit. The drive for the compressor is provided by means of a power takeoff attached to the aperture of the engine gear box of the tractor unitand connected to the compressor via a prop-shaft.

Typically, but not exclusively, screw-type compressors are used. Inorder to achieve the necessary volumetric efficiency, the screws of ascrew compressor must run at relatively high speeds, of the order of7000 to 9000 rpm. However, the maximum speed of the vehicle powertake-off shafts is typically between 1600 and 1800 rpm. Consequently,the speed of the power take-up shaft must be increased by a factor ofapproximately in 4.5 in order to produce the required speed for thecompressor.

Existing screw compressors used on road tankers achieve the step-up bymeans of a very large gear wheel mounted on the power take-off shaftwhich engages with a very small pinion connected to the compressor.However, the large gear wheel takes up a great deal of space, making thecompressor very large and heavy and in some cases making it impossiblefor the compressor to fit inside the chassis of the tractor unit. Insome cases, it is necessary to mount the compressor outside the chassisand to use alternative drives such as hydraulic drives, belt drives,separate engine drives, electric motor drives and the like, which addssubstantially to the cost, weight and maintenance of the installation.

In addition, in recent years, the use of three-axle tractor units hasincreased, reducing still further the space available to mount thecompressor.

Moreover, many haulage operators like to fit larger fuel tanks on thechassis to allow fuel to be bought in the country where it is cheapest.This reduces still further the space available for mounting thecompressor or, alternatively, reduces the size of fuel tanks which canbe mounted on the chassis.

What is needed is a compact compressor assembly.

SUMMARY OF THE INVENTION

The present invention relates to compressors, and more particularly to acompressor assembly.

In general, in one aspect, the invention features a compressor assemblyincluding compressor means having an inlet, an outlet and a means fordrawing air through the inlet and exhausting compressed air through theoutlet, rotary drive input means, and gear means for changing the speedof the rotary drive input means and having an input connected to therotary drive input means and an output driving the compressor means, thegear means comprising planetary gear means.

In another aspect, the invention features a system having a flow pathfor fluid, the system including pump means for pressurizing fluid forflowing along the flow path, cooling means through which the flow pathpasses for dispersing heat from the flowing fluid, a fluid-operatedmotor actuated by the pressurized fluid, and a fan driven by thefluid-operated motor for generating an air current passing over thecooling means.

Other features and advantages of the invention are apparent from thefollowing description, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood by reference to the detaileddescription, in conjunction with the following figures, wherein:

FIGS. 1( a) and 1(b) are a side view and end view respectively of anexemplary screw compressor in accordance with the present invention;

FIG. 2 is a longitudinal cross-section through the exemplary screwcompressor of FIG. 1;

FIG. 3 is a cross-section through the exemplary screw compressor of FIG.1, looking in the direction of arrows X-X of FIG. 2;

FIG. 4 is a schematic representation showing an exemplary operation ofthe exemplary screw compressor of FIG. 1;

FIG. 5 is a schematic representation showing a first variant of theexemplary screw compressor of FIG. 1; and

FIG. 6 is a schematic representation showing a second variant of theexemplary screw compressor of FIG. 1.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

As shown in FIGS. 1 to 4, a screw compressor includes an elongate metalhousing 10 having a base wall 12, two generally parallel side walls 14,16 extending perpendicularly from the base wall, two inclined shoulderportions 18, 20 at the upper end of each of the side walls and a topwall 22 extending parallel to the base wall 12. Two parallel end walls24, 26 extending perpendicularly to the base, side and top walls 10, 14,16, 22 are located one at each end of the housing.

The housing 10 encloses a conventional twin helical screw compressor 28,having two helical screws, one female 28 a and the other male 28 b shownschematically in the drawings, which has an inlet 30 and outlet 32 inthe housing 10. The screw compressor is driven by means of a step-upgear box 34, which is typically driven by a power take-off via propshaft (not shown) of a lorry of other vehicle.

The gear box 34 has two input shafts 36, 38, extending through one ofthe end walls 24 and offset both vertically and horizontally withrespect to each other. Each input shaft 36, 38 is mounted in bearings 42in the housing (only the bearings for the upper shaft 36 are visible inFIG. 2) and each input shaft 36, 38 carries one of two identical spurgears 44, 46 which meshes with the spur gear carried by the other inputshaft, which ensures that both input shafts 36, 38 rotate, irrespectiveof which one is driven.

It will be noted that the upper input shaft 36 and lower input shaft 38rotate in opposite directions. This allows the compressor assembly to beused without modification, irrespective of the direction of rotation ofthe power take-off shaft. In practice, the shaft of the correctrotational sense is connected to the power take-off shaft and the otherunused shaft is covered by a removable cap 40.

The upper input shaft 32 is connected to the carrier 50 of a planetarygear set. Three equally-spaced identical planet gears 52 are rotatablymounted on the carrier 50 by means of bearings 54 and engage with anannulus 56 which is fixed with respect to the housing 10. The planetgears 52 also mesh with a sun gear 58 which is connected to an outputshaft 60 of the planetary gear set P which forms the input to the femalehelical screw 28 a of the helical screw compressor 28. The output shaft60 is mounted in bearings 62 in the housing 10 and carries a spur gear64 which meshes with a spur gear 66 of an input shaft 68 of the malehelical screw 28 b of the screw compressor 28. The male input shaft 68is mounted in bearings 70 in the housing and is aligned parallel to theinput shaft 60 of the female helical screw 28 b. The opposite ends ofthe helical screw conveyors 28 a, 28 b are also mounted in bearings 72,74 in the end wall 26 remote from the input shafts 36, 38.

The spur gear 64 of the input shaft 60 of the female helical conveyor 28a is larger than the spur gear 66 of the input shaft 68 of the malehelical conveyor 28 b, whereby the male helical conveyor 28 a runsfaster than the upper helical conveyor. The step-up ratio in theembodiment described is 5:3, but a different step-up ratio, a step-downratio or a 1:1 ratio may be used instead, depending on the circumstancesand in particular depending on the model of helical screw compressor.

In use, the screw compressor is located in the appropriate position,typically on the tractor unit of an articulated lorry, and inlet andoutput pipes (not shown) are connected to the inlet and outlet 30, 32respectively. A prop-shaft (not shown) connects the power take-off toone of the two input shafts 36, 38 of the required direction of drive(clockwise or anticlockwise). The protective shaft extension cover issecured over the other, “unused shaft”.

To start up the screw compressor, the power take-off is engaged. If thepower take-off shaft is connected to the upper input shaft 36, thecarrier 50, to which the input shaft is connected, is rotated at thesame speed as the input shaft. The interaction of the carrier 50, planetgears 52, fixed ring gear 56 and sun gear 58 produce a step-up ratio,typically of the order of 4.5:1 (although this could be much larger ormuch smaller) and cause the output shaft 60 of the planetary gear set Pto rotate much more quickly than the input shaft 36. The female helicalrotor 28 a rotates at the same speed as the shaft 60 and, by virtue ofthe inter-engaging spur gears 64, 66 on the input shafts 60, 68 of thefemale and male rotors 28 a, 28 b, the male rotor is also rotated.

If the prop-shaft is connected to the lower input shaft 38 (with theprotective shaft extension cover secured over the protruding end of theupper input shaft 36), the carrier 50 is still rotated at the samespeed, by virtue of the meshing of the spur gears 44, 46 on the upperand lower input shafts 36, 38. Operation of the screw compressor istherefore independent of which input shaft 36, 38 is connected to theprop-shaft. However, the rotation of the rotors 28 a, 28 b is fixed bydesign and the power take-off rotation can be clockwise oranticlockwise. It is therefore important that the input shafts 36, 38facilitate rotation in both directions.

The use of a planetary step-up gear set allows the overall size of thecompressor assembly to be compact, which is particularly important ifspace for installation is limited, for example on the tractor unit of alorry.

A first variant of the embodiment of FIGS. 1 to 3 is shown in FIG. 4.The screw compressor is identical to that of FIGS. 1 to 3 and thereforehas only been illustrated schematically. The differences from the firstembodiment relate to the lubrication system.

The lubrication system includes an oil pump 80 driven by the lower inputshaft 38. The pump 80 draws oil via a filter 81 from a sump 82 in thebase of the housing 10 and pumps it out of the housing via a connectinghose 84 to a hydraulic motor 86. A pressure relief valve 88 is alsolocated between the pump 80 and the hydraulic motor 86 in order toprotect the pump for excessively high pressures which can occur, forexample, if the oil is viscous as a result of low ambient temperature atstart-up of the compressor.

The hydraulic motor 86 drives a fan 90 for an oil cooler 92 locateddownstream of the hydraulic motor (although it could be mounted upstreamof the hydraulic motor instead). The cooled oil is then returned to thecompressor housing 10 via a hose 94, and is used to lubricate variouscomponents of the screw compressor in the normal way, via a number offlow restrictors R.

By using a cooling fan which is driven by the pressurized oil, thecooling is not dependent on an external source of power, e.g.electricity, to drive the fan. Moreover, hydraulic systems generallyhave a high reliability, which minimizes the likelihood of breakdownswith the cooling system.

A further variant is shown in FIG. 6. This variant includes all of thefeatures of FIG. 5 and corresponding components have been given the samereference numerals. However, the arrangement of FIG. 6. includes afurther hydraulic motor 96, between the first hydraulic motor 86 and theoil cooler 92, which drives a second fan 98 for an air cooler 100 forcooling compressed air emerging from the air outlet 32 of thecompressor.

The invention is not restricted to the details of the foregoingembodiments. For example, although the embodiments refer to a screwcompressor, other types of compressor could be used instead, for examplea hook and claw compressor. Moreover, although the embodiments areparticularly useful when used on a lorry, the invention is notrestricted to such use and the compressor could be used in otherlocations, such as in general industrial use.

It is to be understood that the foregoing description is intended toillustrate and not to limit the scope of the invention, which is definedby the scope of the appended claims. Other embodiments are within thescope of the following claims.

1. A compressor assembly comprising: compressor means having an inlet,an outlet and a means for drawing air through the inlet and exhaustingcompressed air through the outlet; rotary drive input means; and gearmeans for changing the speed of the rotary drive input means and havingan input connected to the rotary drive input means and an output drivingthe compressor means, the gear means comprising planetary gear means. 2.The compressor assembly of claim 1 wherein the gear means comprisesstep-up gear means.
 3. The compressor assembly of claim 1 wherein theplanetary gear means comprises a carrier connected to the rotary driveinput means, a plurality of planet gears mounted on the carrier andengaging with a fixed annulus and engaging with a sun gear which formsthe output of the planetary gear means.
 4. The compressor assembly ofclaim 1 further comprising a plurality of rotary drive input means. 5.The compressor assembly of claim 4 wherein the plurality of rotary driveinput means rotates together.
 6. The compressor assembly of claim 5further comprising a gear mounted on a first rotary drive input meansengaging with a gear mounted on a second rotary drive input means. 7.The compressor assembly of claim 4 further comprising a first and secondrotary drive input means which are adapted to be rotated in oppositedirections.
 8. The compressor assembly of claim 1 wherein the compressormeans comprises first and second rotary inputs driven by the output ofthe gear means.
 9. The compressor assembly of claim 8 further comprisingfirst and second input shafts driven by the output of the gear means.10. The compressor assembly of claim 9 wherein the first and secondinput shafts of the compressor means are substantially parallel.
 11. Thecompressor assembly of claim 9 further comprising inter-engaging gearsmounted on the first and second input shafts of the compressor.
 12. Thecompressor assembly of claim 11 wherein the ratio of the inter-engaginggears on the first and second input shafts of the compressor means isgreater than
 1. 13. The compressor assembly of claim 1 wherein thecompressor means comprises a helical screw compressor.
 14. A systemhaving a flow path for fluid, the system comprising: pump means forpressurizing fluid for flowing along the flow path; cooling meansthrough which the flow path passes for dispersing heat from the flowingfluid; a fluid-operated motor actuated by the pressurized fluid; and afan driven by the fluid-operated motor for generating an air currentpassing over the cooling means.
 15. The system of claim 14 wherein thefluid-operated motor is in the flow path of fluid.
 16. The system ofclaim 14, further comprising a second fluid-operated motor actuated bythe pressurized fluid.
 17. The system of claim 16 wherein the secondfluid-operated motor is in the flow path of the pressurized fluid. 18.The system of claim 16, further comprising a second fan driven by thesecond fluid-operated motor.
 19. The system of claim 18 wherein thesecond fan is adapted to generate an air current passing over a coolingmeans.
 20. The system of claim 19 wherein the second motor is adapted togenerate an air current passing over a cooling means for a flow offluid.
 21. The system of claim 20 wherein the second fan is adapted togenerate an air current passing over a cooling means for a flow of fluidother than the fluid which operates the second fluid-operated motor. 22.The system of claim 21 wherein the flow of fluid comprises the output ofthe compressor.
 23. The system of claim 22 wherein the output is fromthe compressor of which the flow path of pressurized fluid generated bythe pump means forms part.
 24. The system of claim 14 further comprisingpressure relief valve means in the flow path.